This invention relates, generally, to controllers for electric motors, and more specifically, to controllers for electric motors used in printers.
Computer printers use a variety of motors to actuate pumps, move components, and perform many other functions. In one type of configuration, a Pulse Width Modulated (PWM) signal is supplied to a DC motor. The DC motor may be used, for example, to power a mechanism which primes and purges a printer head. In such an application the mechanism will have a well-defined travel path and pre-set hard stops.
With these conditions, it is important that the PWM signal is sufficient so that the motor moves the mechanism to its various stops. However, if the PWM signal is too strong the motor can move the mechanism too quickly. These movements can cause ink to be thrown from the mechanism or can cause damage to the mechanism or other components.
To control the speed of motors one can employ a proportional integral controller which uses a feedback system based on the motor speed. However, the sensors used to detect the speed can be expensive and can add to the sophistication of the overall system. In low-cost applications these sensors can also create a degree of velocity control and position control which is beyond the requirements of the application. In the printer priming station application one is concerned about the motor velocity being in a proper range. However, precise velocity control and precise position control are not as great a concern as they might be in other applications.
Developments in fuzzy logic can allow feedback decisions to be made in systems by using reference signals which relate to the values being controlled. However, there is a need for the use of fuzzy logic in motor velocity control in a way which is simple and efficient.
To implement the necessary velocity control, it is also desirable to have proper calibration. Ideally, the calibration technique, like the velocity control method, should be simple and inexpensive. This is particularly true for applications which employ inexpensive motor designs such as 3-pole DC motors.
What is needed for the printer priming station and other similar applications is a velocity controller which will provide sufficient velocity control to keep the motor within a range so as to prevent undesirable consequences, but which is simple and relatively inexpensive.
It is an object of the present invention to provide a velocity controller for electric motors which maintains the motor within an acceptable velocity tolerance.
It is another object of the present invention to provide a velocity controller which is simple.
It is another object of the present invention to provide a velocity controller which is inexpensive.
It is another object of the present invention to provide a velocity controller which avoids the use of optical or other sophisticated sensors.
It is another object of the present invention to provide a velocity controller which operates properly in the presence of measurement noise, motor variations, and load variations.
A device for controlling the velocity of an electric motor is provided. The device combines a traditional PI (Proportional+Integral) velocity controller with a robust mapping technique that estimates the velocity of the motor. The mapping technique is based on fuzzy logic methods, and provides a robust estimate of the motor""s rotational velocity by using the motor current measurement and pulse-width modulated (PWM) voltage being applied to the motor.
An advantage of the invention is that it eliminates the need for optical or other more complicated velocity sensors.
A further advantage of the invention is that it provides adequate control of electric motor velocity in a simple way with relatively low cost.
A further advantage of the invention is that it operates properly in the presence of measurement noise, motor variations, and load variations.
These and other objects, advantages, and features of this invention will be apparent from the following description.